We (Loyal Wergedal and Joe Wendtland) started a research project to quantify the amount of pollution in various parts of the Beaver Creek watershed to make sure the clean clear beautiful stream keeps its reputation. To do this we have conducted many different pollution studies on the stream to determine if there is a pollution problem that needs to be corrected or controlled.

So to explain what we have been looking for, the following are questions that we are trying to answer: What pollutants are in the stream and how high of concentrations are they? How does the pollution level change among the three sites on Beaver Creek and how does it change seasonally? Finally, if the stream is polluted, where is the pollution coming from and how can we correct the problem?
 

Evolution

From early studies we know that insects evolved somewhere around the Paleozoic period. They most likely came from a myriapod ancestral line (Ward 29). Water insects evolved on land and then evolved to water (Ward 35). F. M. Carpenter believed that there were four major stages that insects evolved in. The first stage is called Aptergota. These insects were wingless.

The second stage was called the Paleoptera stage. These insects were winged, but lacked the alar articulation necessary to flex their wings back over their body when at rest. There are many different views on why wings have evolved. Carpenter believed that insect wings evolved predation. The air was mostly uninhabited, so it was a likely place for insects to venture. Other reasons may include thermo-regulation as Douglas believed (Ward 30). Some think it was an enhancement of passive dispersal (Ward 30). However, others believe that they were developed for sexual attraction (Ward 30).

The third stage is the Neoptera, which was the development of wing flexing. This gave insects the ability to fold their wings over their abdomen. Furthermore, this adaptation reduced predation by allowing insects to hide in and under small areas quickly. This stage is called Endopterygota because the adaptation evolved totally on the outside of their body.

Finally, the fourth stage is Neoptera, Endopterygota. This stage involved the evolution of holometabolism. In holometabolism the immature stages of insects usually live in different habitats and eat different foods than the adult of that species. This adaptation was "a form of intraspecific niche segregation (Ward 30). "The developing wings of the endopterygotes invaginate into the larval body and the last larval instar becomes the pupil stage (Ward 30). It has been proposed that body structures called spiraclar flaps, which were supposedly developed for controlling respiratory water loss, were the precursors of gills. The spiracles were apparently present on all body segments. The spiraclar flaps may have allowed insects to enter water. "Paleozoic Mayflies likely possessed gills and spiracles on all body segments (Ward 30).
 

Life Cycles
 

When identifying life cycles of insects one must understand that there is three main types of life cycles. The cycles are called seasonal cycles. Seasonal cycles have distinct changes of larval sizes that occur with time. The three cycles are slow seasonal cycle, fast seasonal cycle, and non seasonal cycle. The duration of these life cycles can last less than two weeks to a year long life cycle. Other factors such as climate also fit in to the scheme as to how long these cycles last.

Slow seasonal cycles are common in cool streams. Usually Plecoptera, Ephemeroptera, and Trichoptera are associated with this life cycle (N.H. Anderson and Wallace, 43). Eggs hatch soon after deposition. The organism grows slowly in winter. These insects are usually mature in a years time (N.H. Anderson and Wallace, 43). In addition, they usually have a flight period early in the year.

Another cycle is called fast seasonal cycle. During fast seasonal cycles insects grow rapidly after a long egg or larval diapause or a form of hibernation (N.H. Anderson and Wallace, 43). Some fast seasonal cycles achieve full term in spring, early, and late summer. The rapid growth in warm weather for some of these insects give them a smaller size.

The third life cycle is called a non-seasonal cycle. Several stages and size classes are present in all seasons associated with non-seasonal cycles. Some life cycles' spans even last longer than a year. Unfortunately, there is no determined time that a insects takes to mature because the insects are very diverse and spread out in different climates.
 

Substratum
 

Although insects are present in every stream, there are a few major determinants that effect the distribution and abundance of aquatic insects. The first major factor in this equation is substratum. Substratum material at the bottom of a stream such as rocks and sand. This can vary from silt to pebbles to boulders. In several studies larger substratum tends to have a larger abundance and variety of aquatic insects than a small type of substratum (Resh and Rosenberg 363). This knowledge was gained from experiments in laboratories with very consistent sized substratum. In natural conditions large substrate, which can hold a large variety of substratum, will tend to have a larger abundance of insects up to a cobble sized substrate (Resh and Rosenberg 364). The composition of average substrate size in relation to the whole stream decreases from the headwaters to the mouth of the stream because of the substrate the current carries (Ward 237). Large substrate also holds more organic material in it (Ward 268).

Another important factor of substratum is the organic material trapped by it. Organic material is the result of decomposed leaves and other dead plants. The amount of organic material directly affects the number of herbivorous insects and that indirectly affects carnivorous insects. This is because most herbivorous insects feed on organic material. A low amount of organic material will create competition that will lower herbivorous insect populations (Resh and Rosenberg 378). Fewer insect prey will in turn also lower carnivorous insect populations. In addition, organic levels that are too high will result in lower insect populations (Resh and Rosenberg 378). Also, organic material needs to be in small pieces (<1mm.) to benefit insects (Resh and Rosenberg 378). Organic material is especially important to caddis flies that make cases about themselves out of their surrounding environment. Some species of caddis flies are very selective of the materials that they use. Caddis flies have been found to favor substrates with abundant organic material (Resh and Rosenberg 378). There are several free living caddis fly species, but they may have an evolutionary connection to dwelling in high organic material substrates.

Another important factor is the presence of silt in a stream. In studies that De March has done, she has concluded that silt has more impact on insect populations than substratum size if silt is present in significant amounts (Resh and Rosenberg 377). A stream with heavy silting will decrease the insect diversity and growth which was shown in Chutter's experiments. A study to verify this statement was conducted by Luedtke et al. who removed the fine sediments (silt) from Emerald Creek in Idaho. After doing this he noticed an increase in overall diversity and population of aquatic insects (Resh and Rosenberg 377). However, minor silting (<1mm.) in streams have shown no significant effects on aquatic insects (Resh and Rosenberg 377).

Finally, one major stress on a stream substrate is logging. More specifically the logging roads instead of the actual logging is what contributes an excessive amount of sediment to the stream substrate (Resh and Rosenberg 569). "Compared to an undisturbed control watershed, the mean annual sediment yield was increased only 3.3 times without roads, but was increased 109 times in a patch-cut watershed with roads (Resh and Rosenberg 569)." This sediment loading has been found to affect population and diversity of aquatic insects. A reduction was found from one to five years after logging (Resh and Rosenberg 516). A suggestion by Resh and Rosenberg to protect streams from logging is to make a 30 to 60 meter buffer strip in logging areas (516).

From studies of substratum it is evident that the habitat of aquatic insects directly influences their population, diversity, and growth productivity.
 

Chemical part
 

"Among the most important modifiers of an insect's response to substratum are water temperature, flow regimen, and chemical composition of water. . .(Resh and Rosenberg 379)."

Temperate is another underlying factor in insect viability. "Sweeney and Vannote (1981) suggest that temperature affects growth and controls the endocrine system of insects, which in turn determines the ultimate size and reproductive capacity of the adults (Resh and Rosenberg 380). A low temperature will lower the metabolic rate of the insect which in turn slows the growth rate and reproductive ability. The longer an insect requires to reproduce, the fewer there will be present in the stream. Stunted growth will also limit the number of progeny the insect will be able to produce. You may expect high temperatures to be advantageous to aquatic insects because it raises their metabolism, but it is not. Increased growth rate is a negative affect since it favors the male insects. The emergence can limit chances of reproduction. A study done by Nebeker in 1971 on ten aquatic insect species showed that thermopollution can result in insect emergence as much as four to five months earlier than usual (Resh and Rosenberg 521). High temperatures often increase the effects of chemicals in the water on aquatic insects (Resh and Rosenberg 525). According to Whitney in 1939, lethal levels of heat for some Plecoptera and Ephemeroptera is 20 degrees Celsius (Resh and Rosenberg 519). Garten and Gentry in 1976 reported that Odanata have a higher tolerance to temperature and can withstand 40 degrees Celsius temperatures. Overall, temperatures above 30 degrees Celsius will cause a reduction in population, density, production, and growth of aquatic insects (Resh and Rosenberg 520). Moderate heating (<25 degrees Celsius) will have positive effects on the production and growth without affecting population (Resh and Rosenberg 520). On the other hand a lower temperature than normal will lower the metabolism (Resh and Rosenberg 380). In nature there are a few major temperature fluctuations such as during winter and summer that keep the insects' "body clock" on schedule. If the temperature doesn't vary like it usually does it could negatively affect population and diversity of aquatic insects (Resh and Rosenberg 521). Studies have shown that normal fluctuations of temperature allow eggs to hatch quicker than the mean temperature without fluctuations (Ward 219). Fluctuations are especially important for eggs that diapause before they hatch (Ward 220).

According to J. V. Ward most spring fed streams are within one degree Celsius of the average air temperature (201). Most insects go into dormancy and out of it during the winter by the changes of water temperature (Ward 220). One may think that if a stream freezes solid that all the organisms will die. However, many species of Chironomids and Trichoperans can survive being completely frozen for over five months (Ward 222). In fact, many aquatic insects grow at or near zero degrees Celsius (Ward 211).

Another factor in insect viability is the pH of the stream. It usually increases from the headwaters of a stream to the lower reaches of the stream (Ward 346). Most unpolluted streams have a pH of 6.0-9.0 (Ward 346). PH of below 6.0 is considered acidification of the stream. Acidification usually results in low diversity and low productivity of aquatic insects (Resh and Rosenberg 531). PH less than 6.0 will kill some Ephemeroptera and Plecoptera species (Ward 348).

"The volume of flow, the relationship of velocity to depth, the periodicity in timing of high and low flow, and so forth, can have important effects on the particle size, composition, and relative stability of the substratum. . . (Resh and Rosenberg 380)." A strong current will first of all make the substrate a larger mean size than a slow current and sediment loading will have more effects on a slow water current (Ward 268). The speed of the water flow indirectly affects the aquatic insects. The flow of the water will determine the particle size, composition, and stability of the substratum (Resh and Rosenberg 380). Therefore, rapid water will have large sized substratum, which tends to be advantageous to insects, but it will limit the amount of captured organic material which will be negative to insects (Resh and Rosenberg 382).

Chemical pollution is the last factor affecting insect fatalities. The first and most important chemical is dissolved oxygen (DO). Insects require DO to breathe, so low concentrations of it will be fatal to aquatic insects. Most DO accumulates in the stream water by diffusion which is a slow process unless it is accelerated by high water current ripples. Therefore, high current velocity is important in areas were DO concentrations are already low (Ward 335). DO concentrations tend to lower during the winter since ice stops the diffusion of air into the water (Ward 332).

Other chemicals will generally give negative effects to the stream. Extreme amount of chemicals dissolved into water is called eutrophication. With a higher amounts of chemicals plants will thrive. In turn, these plants eventually die and create higher amounts of organic material that use up dissolved oxygen during the decomposition process. That is how high levels of nutrients can affect aquatic insects. However, a slightly higher nutrient level in water will be an advantage to aquatic insects because it will supply them with more food and habitat ( Resh and Rosenberg 511).

Insects play an important role in removing nutrients from the polluted waters. When insects emerge from the water as adults they remove some of the nutrients that were in the water. Studies have found that they remove 1-14 percent of Phosphorus and 1-10 percent of Nitrogen from the water (Resh and Rosenberg 151).

By knowing some of the important factors in aquatic insect fatalities, people will be more able to correct pollution problems of streams to keep the insects from dying out forever.

This paper gives background information to our study of pollution in Beaver Creek. In order to figure out the pollution we must conduct tests to determine how much pollution there is present in the stream.

In achieving this we used the FBI (Family Level Biotic Index) test. The test deals with the tolerance that insects have to pollution. In conducting these tests we must first understand the insects themselves. More specifically, we must understand their evolution, life cycle, and preferred habitats. In addition, we should also understand how chemicals, temperature, and stream velocity affects these organisms.

For Information on species of fish from Beaver Creek see the Beaver Creek Fish Page